Frequency-stabilizing system



March 1, 1949.' G. G. BRUCK ET AL FREQUENCY STABILIZING SYSTEM Filed March 18, 1946 S hm. @s Qw Patented Mar. 1, 1949 FREQUENCY -STABILIZING SYSTEM `George G. Bruck, East Orange, N. J., and PaulJ.

Pontecorvo, Cambridge, Mass.,

assignors to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application March 1s, 194s, serial No. 655,074

(ci. 25o-3s) 14 Claims.

This invention relates to frequency-stabilizing systems, and constitutes an improvement over the system disclosed in the copending application of George G. Bruck and Philip E. Volz, entitled Frequency stabilizing system, Serial No. 647,008, filed February 12, 1946.l

While not limited thereto, the present invention is admirably adapted to the control of the carrier wave of a communication system, such as is disclosed in the copending application of George G. Bruck, Philip E. Volz, Paul J. Pontecorvo and Malcolm C. Vosburgh, entitled Radio communication system, Serial No. 650,716, filed February 27, 1946, and comprising, for example, two Widely separated terminal stations and a plurality of intermediate relay stations, the system permitting the two-way transmission of intelligence between any and all of the stations included therein, with the carrier wave emanating from each relay station under the control of the carrier wave received at each relay station, and all under the master control of the carrier wave originating at one of the terminal stations.

In the frequency-stabilizing system disclosed in the first of the above referred to copending applications, reflections, within the system, of energy from certain of the components thereof have been found to interfere with the efficient functioning of other of said components. In addition, said system has been found to be so sensitive that its initial adjustment becomes unduly critical and presents impedance-matching problems which are dicult of solution.

It is, therefore, an object of the present invention to so decouple the various components thereof as to eliminate the eects of energy reflected thereby.

It is another object of the present invention to simplify the procedure for initially setting up the system.

It is still another object of the present invention to simplify the impedance-matching problems thereof.

These, and other objects of the present invention, which will become more apparent as the detailed description thereof progresses, are attained, briefly, in the following manner:

A portion of a carrier wave, which may have a frequency. say, of 10,000 mc., and which is to be frequency stabilized. is divided into two parts, one cf which is amplitude modulated at a relatively low frequency, say, 50 mc., and the other of which is transmitted through a cavity resonator whose natural resonant frequency constitutes a reference frequency corresponding to the mean frequency desired of said carrier wave. The amplitude-modulating means are, preferably, such that the carrier wave itself is suppressed, and only the resultant sidebands subsequently utilized. By so doing, as will hereinafter become more apparent, the effects of energy reflections and impedance mismatches between the componentsl of the system are eliminated.

The lengths of the paths of the portions of the carrier wave which are amplitude modulated and applied to the cavity resonator, respectively. are

. made to differ, preferably, by 11i/4 where `n is an odd integer and A is the wave-guide wavelength corresponding to the frequency desired of the carrier wave. As a result of this difference in length, when the sdebands produced as aforesaid and a portion of the carrier wave coming from the cavity resonator are combined in a mixer, the effect is the same as combining a portion of the carrier wave which is varying in amplitude at the modulation frequency with a portion of the carrier wave which is of constant amplitude but out of phase with said rst portion, and produces a substantially constant-amplitude resultant wave, provided the frequency of the carrier wave corresponds to the hereinbefore referred to reference frequency, that is, to the natural resonant frequency of the cavity resonator. 1f, on the other hand, the frequency of the carrier wave has drifted from the frequency desired thereof, the sidebandsand the carrier wave coming from the cavity resonator do not meet at the mixer in phase quadrature, and. therefore, the in-phase components of said sidebands cause the resonator-transmitted, carrier-wave portion to become substantially amplitude modulated.

The modulation envelope of the last-named re sultant wave-has a phase, relative to the amplitude modulation initially applied to the carrier,

Wave, and a magnitude, which are functions, respectively, of the sense and magnitude of any deviation of the frequency of said carrier wave from the reference frequency. Preferably, said modulation envelope is either ir phase with said initially applied modulation, or it is in phase oppoor in phase opposition thereto, is recovered, the

magnitude of said deviation.

sense and 'magnitude'of the recovered envelope being functions, respectively, of the sense and The recovered modulation envelope is comv bined, for example, in a differential-amplitude detector, with a portion of the initially applied moduquency, and having an audio-frequency compo,

nent corresponding to any intelligence which might have been initially impressed upon said carrier wave. The output of the differentialamplitude detector is passed'through a low-pass ilter to remove the audio-frequency component thereof, and the remaining D.C. or unidirectional component is applied, through a buffer amplifier, to any rpreferred electronic or mechanical tuning contro to adjust the frequency of the carrier wave/to compensate for the deviations above referred to.

In the accompanying specification there shall be described, and in the annexed drawing shown, an illustrative embodiment of the frequency-stabilizing system of the present invention. It is, however, to be clearly understood that the present invention is not to be limited tothe details herein shown and described for purposes of illustration only, inasmuch as changes therein may be made without the exercise of invention, and within the true spirit and scope of the claims hereto appended.

In said drawing, the single figure is a partial block, partial schematic diagram of a frequencystabilizing system assembledin accordance with the principles of the present invention.

yReferring now more in detail to the aforesaid illustrative embodiment of the present invention,

with particular reference to the drawing illustrating thesame, thenumeral ||I designates an oscillator for generating a carrier wave wn, preferably, in the microwave region oi the electromagnetic spectrum. Itis the mean frequency of this carrier wave that it is desired to stabilize, and for this purpose there is provided any appropriate frequency control adapted to respond to a control signal generated as will hereinafter be fully described.

A portion of the output of the oscillator I is conveyed, through a wave guide I2, to a matched load, for example, al suitable antenna for radiating the same.

Anothervportion of the output of the oscillator I0 is applied to the so-called- E arm I3 of a wave-A guide assembly |4 known as a magic T. Such a wave-guide assembly comprises. in addition to the E arm I8, a pair of collinear side branches l5 and I6 extending at right anglesto said E arm I3, and a so-called H arm i1 extending outwardly from said side branches I5 and I8, mutually Del.-

pendicular thereto and to said E arm, said E arm, said side branches, and said H arm all extending from a common junction I8., As shown in the drawing, the H arm .|1 recedes 'from the observer for a short distance from the common junction I8, then bends downwardly, and is then twisted through an angle of 90.

The energy traveling along the E arm I3 splits at the junction |8, part traveling along the side branch I5, part traveling along the side branch I8, and part traveling along the H armA I1 which is terminated in a. matched load I 9. I

The side branch I6 communicates with the E arm 20 of another magic T" 2| including side branches 22 and 23 and an H arm 24, all extending from a common junction 25, and the side branch I6 communicates, through a Wave guide 26 incorporating a "line stretcher 21 for adjust.- ing the electrical length thereof, with a cavity resonator 28 the natural resonant frequency wn of which constitutes the reference frequency with respect to which it is desired to maintain the frequency of theV 'oscillator I0 in a ilxed relationship.

The side branches 22 and 28 of the magic T" 2| terminate in oppositely-disposed crystals 29 and 30, vbetween one side of each` of 'which and the magic T itself capacitance 3| and 32 exist, vthe wave-guide system, generally, Abeing grounded,. as at 83, and said crystals being connected, in series with a source 34 of direct current and a.` resistor 35,' to provide parallel inputs to ground through a capacitor 36 and the secondary winding 31 of a radio-frequency transformer 38. The primary winding 89 of the transformer 38 is connected to an oscillator 40 adapted to generate relatively low, radio-frequency en-g ergy w1 for amplitude modulating the carrier wave w15. The frequency of the modulating energy may be, for example, 50 mc.

The magic T 2| -functions as a balanced modulator as disclosed in detail in the copending application of Paul J. Pontecorvo, entitled Modulator, Ser. No. 652,738, filedI March 7, 1946. llhe carrier wave w11 travelingalong the arm 20 toward the junction 25, with or without locallygenerated intelligence we, splits at said junction, part traveling along theside branch 22 toward the crystal 29, and part traveling along the side branch 23 toward the crystal 30. The oppositelytraveling parts of the carrier wave incident upon said crystals are. it will be noted, 180 out of phase,.and each becomes amplitude modulated by the energy'injected into said crystals, in parallel, from the oscillator 40. Thus, sidebands, having frequencies equal to the sum ofand difference between the frequencies of the carrier and modulation Waves, are produced at the crystais- 29 and 30, Which sidebands, together with any carrier components resulting from mismatch-V ing of the crystals to the wave-guide system,l

travel back along the side branches 22 and 23 to ward the junction 25. The sidebands, upon reaching said junction, travel along the H arm 24 of the magic T 2|, but the reflected carrierwave components, being in phase opposition, are cancelled along said H arm 24, so that the final output of the magic T 2| is a carrier sup` pressed, amplitude-modulated wave.

'Ihe sidebands comprising said last-named wave areconveyed, through'a .wave guide 4|, to the E arm 42 of another magic T 43 which, like that previously described, includes side branches 44 and 45 and an H arm 46, all extendingv from aA common junction 41. The side branches 44 and,

45 are terminated in crystals 48 and 49,' between one side of each of which and the magicT itself, capacitances 50 and 5| exist, said magic T being grounded, and said crystals being oo nnected, in series with a source 52v of direct current and a resistor 53, to provide parallel outputs to ground through a capacitor 54 and the primary winding 55 of a radio-frequency transformer 56. The H arm 46 of the magic Ty 43 is connected, through a wave guide 51, to the output'side of thecavity resonator 28.

By adjusting the "line stretcher 21, the electrical lengths of the paths taken by theV energy traveling from the Junction Il of the magicf I4 to the junction 41 of the magic T" 43,'through the balanced modulator magic T 2| on the one hand, and throughthe cavity resonator on the other, are made to differ by 11A/4, where n is an odd integer and i is the wave-guide wavemagnitudeEto thefre'q'u c yct'iftrol length corresponding to the natural resonantv frequency of the cavity resonator 28, in other words, to the mean frequency desired of the carrier wave coming from the oscillator I 0,

Now, at the junction 41 of the magic T 43 which, as will now be described, functions' as a balanced demodulator and a buffer isolating the balanced modulator magic T 2l from the cavity resonator 28, the sideband wavestraveling along the E arm 42 split, part traveling along the side branch 44 toward the crystal 48, andpart traveling along the side branch 45 toward the considered as a vector rotating in the same direction at a frequency of the carrier wave minus that of the modulation wave. These two vectors, rotating at different frequencies, periodically become in phase, and so, they may be considered as oppositely-rotating vectors combining to produce a non-rotating vector constituting a resultant sideband. The latter is, actually, the carrier wave varying in amplitude at the modulation frequency, and when combined, in each of the crystals 48 and 49, with carrier-wave portions coming from the cavity resonator 28, with which they are 90 out of phase, the amplitudes of said carrier-wave portions remain substantially unaffected. Therefore, no modulation envelopes are recovered at the crystals 48 and 49.

However, should the oscillator I0 drift, so that l the frequency of the carrier wave differs from the reference frequency, that is, from the natural resonant frequency of the cavity resonator 28, the latter causes the phase of the carrier wave transmitted therethrough to the balanced demodulator magic T 43 to shift in a direction and to an extent depending. respectively, on the direction and extent of the frequency drift. Hence, at the crystals 48 and 49, the sideband resultant waves and the carrier-wave portions coming from the cavity resonator 28 are no longer in phase quadrature, and as a result, inphase portions of said sideband resultant waves cause said carrier-wave portions to become amplitude modulated.

If the frequency of the carrier wave generated by the oscillator l0 drifts above the reference frequency, the carrier-wave portions coming from the cavity resonator 28 acquire amplitude modulation, and if said frequency drifts below the reference frequency, said carrier-'wave portions acquire amplitude modulation."

In any event, the modulation envelopes thus produced are recovered across the crystals 48,y

' said selected lamplit11de vch It now remains to extract from the outputA of "'lator 'IUI' For this purpose, [the secondary 4 ing`58` of'. thetransfoi'riier iiszconnec amplifier 59 which `is 4 tuned to ,the frequency m entitled Frequency stabilizing system.

of the meduiaupn escalator `4a.; e'The,surprit Abf in@ armani@` (5,9y Vis Qappned; to ,a ',cfifrereiitialamplitude detector Sil4 to whchthere isalsoapplied a portionfof `the outputvofthemodul'ation oscillator 4c. suchj ya Idinerentiai,-miipin:'udcI lietector may, forV example, befsimilanto .thehone disclosed in k,the above referred `to'cop/eiidingapplication of George G.` Bruck,` andA Philip 4E.` Yolnz,

The differential-amplitu detector 8,8 isvfso designed that, in thejcasefwhere ,thev oscillatorl In has not drifted at an; 'andgasaresu1t` no modulation' 'envelope' appears across the transformer v5,6, y,said detector,V has. a ,balanced output which cancelsv itself. Saiddetector is nsor further designed that, in the case'Y where thefoscillator l0 has drifted, and, as `a result, fa modulation envelope does appear across the transf,,orn'ieryy 58, said detector produces al unidirectional `output whose sense and magnitude arefunctidns, respectively,V of ftheA senseand magnitude 0f said drift.

In order to remove'from the output of the differential-/amplitude detector any-.intelligenceoy which may `have 'been vinitially ,impressed upon the carrier wave wh, saidoutputis rai'iplieito a low-pass lter 6|, thereby obtainingfa' iinalrDfC. output. This output is ,then applied.' through a buffer amplifier B2, tothejtu'ning controlli] to compensate `for any vdrift in the'v oscillator, IL".

This completes the'description-,of` the vaforesaid illustrative embodimentfof'tlie present ine vention, includingl the mode of operationthereof. It will be noted from all ofk the foregoingthat the present invention enables. thev stabilization of a carrier wave4 `within very, 'close limits. Furthermore, it enablestheelimination ofthe effects 'of energy reflected between, the various components thereof, land itdsimpliiies the im? pedance-matching problems of thefsystemfwhich, in turn, simplifies thypi'ocedureffr initially settingupthesyst'em."

'Other objects and advantagesjwofMthepresent invention will readily occurto those 'slr'illeI in the art to which the saine relates.,

Wheels claimedris:`

L'Apparatus for stabilizing the frequencyyo'f a carrier wave comprising; means/rceptive of a portion of said carrierWaye, kforso'arriplitu,de modulating' the same as to Vsuppress the car components yof th'e resulting sidebandfwat"y means, receptive of another portion` lof v,sfa`.id car-'Q rier wave, for shifting` the phase Athereof through such an angle that,"upor1 combination of said sideband waves`V and said jphaseeshifted glcarrier wave portionj'a wave having a'"selected'aliiplituel characteristic results;V means, responsiveftofany drift in the frequency of s'aid`,carrier wayam altering the phase of said phase-shifted carrier;y wave portion;" means` for"corribiriirig` said` 'sideband Waves randwsaid' phase hiftedcarrier-wave portionV whereby,` intheffev M event a.` frequency drifty has` occurred," `th resultf, antjwaye has a,substantiallydifferent ,A characteristic rrieansy for deriviri`g`from` named resultant wavea'fWVhi, tude characteristic l which "is" a 'functi dierence between the amplitude characteristics of both said resultant waves; and means, recep- 8 v .I tude characteristic which is a function oi the. difference betweenv the amplitude characteristics of both said resultant waves; and mean'sreceptive said first-'named constituent waves reflected from l said last-named means, for so combining `the same as to suppress the carrier componentsl thereof; means receptive of another portion of Asaid can'ier wave, for shifting the phase thereof through such an angle that, uponcombination of "said sideband waves and said phase-shifted car- 'rier-wave portion, a wave having a selected amplitude characteristic results; means, responsive to any drift in the frequency of said carrier wave,

for altering the phase of said phase-shifted carrier-wave portion; means for combining said sideband waves and said phase-shifted carrier-wave lportion whereby, in the event no frequency drift has occurred, the resultant wave has the aforesaid selected amplitude characteristic, and in the event a frequency drift has occurred, the resultant wave has a substanti-ally dierent amplitude characteristic; means for deriving from said last-named resultant wave a wave-having an amplitude characteristic which is a yfunction'of the diiference between the amplitude?characteristics of both said resultant waves; and means, recep- -tive of said difference-characteristics wave, for

so tuning the source of said carrier wave as to compensate for said frequency drift.

3. Apparatus for stabilizing the frequencyl of' a carrier wave comprising: a wave-guide section, having a. perpendicularly extending branch arm receptive of a portion of said carrier Wave, for deriving from said carrier-wave portion two constituent waves; a pair of non-linear impedances terminating the opposite ends of said wave-guide section, receptive of a modulation wave and said constituent waves, for deriving from the former two additional constituent waves, and combining the same, respectively, with said first-named constituent waves whereby sideband waves are produced; a second branch arm extending perpendicularly from saidv wave-guide section, perpendiculariy to said first-named branch arm, receptive of said sideband waves and portions of said irstnamed constituent waves reiiected from said nonlinear impedances, for so combining the same as to suppress the carrier components thereof: means, receptive of another portion of said carrier wave, for shifting the phase thereof through suchan angle that, upon combination of said sideband waves and said phase-,shifted carrierwave portion, a wave having aselected amplitude characteristic results; means, responsive to any drift in the frequency of said carrier wave, for

Y altering the phase of said phase-shifted carrierwave portion; means for combining said sideband waves and said phase-shifted carrier-wave portion whereby, in the event no frequency drift has occurred, the resultant wave has the aforesaid selected amplitude characteristic, and in the event a frequency drift has occurred, thev resultant wave has a substantially different amplitude characteristic; means for deriving from said lastnamed resultant wave a wave having an ampliof said4 difference-characteristics wave, for :so tuning the source of said `carrier wave as to compensate for said frequencydrift. s v ."f.

4. Apparatus forstabilizing the frequency of a carrier wave comprising: means, receptive of a portion of said carrier wave, for so amplitude modulating the' same as to suppress the carrier components of the resulting sideband waves;-

means, receptive of another portion of said carrier wave, for shifting the phase thereof through such an angle that, upon combination of said sideband waves 'and said phase-shifted carrierwave portion, a wave having a selected amplitude characteristic results; a cavity resonator, resonant t0 the frequency desired of said carrier wave and receptive of said phase-shifted portion thereof, for altering the phase of said phaseshifted portion in response to any drift from said desired frequency; means for combiningsaid ,sideband waves and said phase-shifted carrierwave portion whereby, in the event no frequency -drift has occurred, the resultant wave. has the vaforesaid selected amplitude characteristic, and

in the event a frequency drift has occurred, the resultant wave has a substantially different amplitude characteristic; means for deriving from said last-named resultant wave a wave having an amplitude characteristic which is a function of the difference between the amplitude characteristics of both said resultant waves; and

means, receptive of said difference-characteristics wave, for so tuning the source of said carrier wave as to compensate for said frequency drift.

5. Apparatus for stabilizing the frequency of a carrier wave comprising: means, receptive of a portion of said carrier wave, for deriving therefrom two constituent waves; means, receptive of a modulation wave and said constituent waves, for deriving from the former two additional constituent waves, and combining the same, respectively, with said first-named constituent waves whereby sideband waves are produced; means, receptive of said sideband waves and portions of vsaid first-named constituent waves reflected from said last-named means, for so combining the same asl to suppress the carrier componentsl thereof; means, receptive of another portion of said carrier wave, for shifting the phase thereof through such an angle that, upon combination of said sideband waves .and said phase-shifted carrier-wave portion, a wave having a selected amplitude characteristic results; a cavity res-` onator, resonantto the frequency desiredof said carrier wave and receptive of said phase-shifted portion thereof, for altering-the phase of said phase-shifted portion in response toany drift from said desired frequency; means for combining said sideband waves and said phase-shifted carrier-wave .portion whereby, in the event no frequency drift has occurred, the resultant wave has the aforesaid selected amplitude' characteristic, and in the event a frequency drift has occurred,

the resultant wave has a substantially different amplitude characteristic; means for deriving from said last-named resultant wave a wave having an amplitude characteristic which is a function of the difference. between the amplitude characteristics of both said resultant waves; and means, receptive of said d iiTerence-characteristics wave, for so tuning the source of said carrier wave as to compensate for said frequency drift.

6. Apparatus for stabilizing the frequency'of a carrier wave comprising: a waveguide section, having a perpendicularly extending branch arm receptive of a portion of said carrier wave, for deriving from said carrier-wave portion two constituent waves; a pair of non-linear impedances terminating the opposite ends of said wave-guide section, receptive of a modulation wave and said through such an angle that, upon combination of' said sideband waves and said phase-shifted car- Iier-wave portion, a wave having a selected amplitude characteristic results; a cavity resonator, resonant to the frequency desired of said carrier wave and receptive of said phase-shifted portion thereof, for altering the phase of said phase-shifted portion in response to any drift from said desired frequency; means for combining said sideband waves and said phase-shifted carrier-wave portion whereby, in the event no frequency drift has occurred, the resultant wave has the aforesaid selected amplitude characteristic, and in the event a frequency drift has occurred, the resultant wave has a substantially diierent amplitude characteristic; means for deriving from said last-named resultant wave a wave having an amplitude characteristic which is a function of the difference between the amplitude characteristics of both said resultant waves; and means, receptive of said difference-characteristics wave, for so tuning the source of said carrier wave as to compensate for said frequency drift.

'7. Apparatus for stabilizing the frequency of a carrier wave comprising: means, receptive of a portion of said carrier wave, for so amplitude modulating the'same as to suppress the carrier components of the resulting sideband waves; means receptive of another portion of said carrier wave, for shifting the phase thereof through such an angle that, upon combination of said sideband waves and said phase-shifted carrierwave portion, a wave having a selected amplitude characteristic results; means, responsive to any drift in the frequency of said carrier wave, for altering the phase of said phase-shifted carrierwave portion; means, receptive of said sideband waves and said phase-shifted carrier-wave portion, for deriving from the former, constituent waves of opposite phase, and from the latter, constituent waves of similar phase; means, receptive of said oppositely and similarly phased constituent waves, for combining the same whereby, in the event no frequency drift has occurred, the resultant wave has the aforesaid selected amplitude characteristic, and in the event a frequency drift has occurred, the resultant wave has a substantially different amplitude characteristic; means for deriving from said last-named resultant wave a wave having an amplitude characteristic which is a function of the difference between the amplitude characteristics of both said resultant waves; and means, receptive of said difference-characteristics wave, for

i0 so tuning the source 'of said carrier wave as to compensate for said frequency drift.

8. Apparatus for stabilizing the frequency of a carrier wave comprising: means, receptive of a portion of said carrier wave, for deriving therefrom two constituent waves; means, receptive of a modulation wave and said constituent waves, for deriving from the former two additional constituent waves, and combining the same, respectively, with said rst-named constituent waves whereby sideband waves are produced; means, receptive of said sideband waves and portions of said first-named constituent waves reected from said last-named means, for so combining the same as to suppress the carrier components thereof; means, receptive of another. portion of said carrier wave, for shifting the phase thereof through such an angle that, upon combination of said sideband waves and said phase-shifted ycarrier-wave portion, a wave having a selected amplitude characteristicv results; means, responsive to any drift in the frequency of said carrierwave, for altering the phase of said phaseshifted carrier-wave portion; means, receptive of said sideband waves and said phase-shifted carrier-wave portion, for deriving from the former, constituent waves of opposite phase, and from the latter, constituent waves of similar phase; means, receptive of said oppositely and similarly phased constituent waves, for combining the same whereby, in the event no frequency drift has occurred, the resultant wave has the aforesaid selected amplitude characteristic, and in the event a frequency drift has occurred, the

. resultant wave has a substantially different amplitude characteristic; means for deriving from said last-named resultant wave a wave having an amplitude characteristic which is a function of the difference between the amplitude characteristics of both said resultant waves; and means, receptive of said difference-characteristics wave, for so tuning the source of said carrier wave as to compensate for said frequency drift.

9, Apparatus for stabilizing the frequency of a carrier wave comprising: a wave-guide section, having a perpendicularly extending branch arm receptive of a -portion4 of said carrier wave, for deriving from said carried-wave portion two con'- stituent waves; a pair of non-linear impedance terminating the opposite ends of said wave-guide section, receptive onf a modulation wave and said constituent waves, for deriving from the former two additional constituent waves, and combining the same, respectively, with said first-named constituent waves whereby sideband waves are produced; a second branch arm extending perpendicularly from said wave-guide section, perpendicularly to said first-named branch arm, receptive of said sideband waves and portions of said first-named constituent waves reflected from said non-linear impedances, for so combining the same as to suppress the carrier components thereof; means, receptive of another portion of said carrier wave, for shifting the phase thereof through such an angle that, upon combination of said sideband waves and said phase-shifted carrier-wave portion, a wave having a selected amplitude characteristic results; means, responsive to any drift in the frequency of said carrier wave, for altering the phase of said phase-shifted carrier-wave portion; means receptive of said sideband waves and said phaseshifted carrier-wave portion for deriving from the former, constituent waves of opposite phase, and from the latter, constituent waves of similar phase; means-Vy receptive ofsaid oppositely and drift has occurred, the resultant wave has. the

aforesaid selected amplitude characteristic, and in the event a frequency drift has occurred, the resultant wave has a substantially different amplitude characteristic; means for deriving from said last-named resultant wave a wave having an amplitude characteristic which is a function of the difference between the amplitude characteristics of both said resultant waves; and means, receptive of said difference-characteristics wave, for so tuning the source of said carrier Wave a to compensate for said -frequency drift.

10. Apparatus for stabilizing the frequency of a carrier wave comprising: means, receptive of a portion of said carrier` wave, for so amplitude modulating the same vas to suppress the carrier components of the resulting sideband waves; means, receptive of another portion of said car- -rier wave, for shifting the phase thereof through such an angle that, upon combination of said sideband Waves and said phase-shifted carrier- .wave portion, a wave having a selected amplitude characteristic results; a cavity resonator, resonant to the frequency desiredof said carrier wave and receptive of said phase-shifted portion thereof, for altering the phase of said phaseshifted portion in response to any drift from said desired frequency; means, receptive of'said sideband Waves and said phase-shifted carrier-wave portion, for deriving from the former, constituent waves of opposite phase, and from the latter, constituent waves of similar phase;- means, receptive of said oppositely and similarly phased constituent waves, for combining the same whereby, in the event no frequency drift has oc-;

curred, the resultant wave has the aforesaid selected amplitude characteristic, and in the event a frequency drift has occurred, the resultant wave has a substantially diiferent amplitude characteristic; means for deriving from said lastnamed resultant wave a wave having an amplitude characteristic which is a function of the diiference between the amplitude characteristics of both said resultant waves; and means, recep-` tive of said difference-characteristics wave, for

so tuning the source of said carrier wave as to` l) l1. Apparatus for stabilizing the frequency of 1 compensate from said frequency drift.

a carrier wave comprising: a wave-guide section, having a perpendicularly extending branch arm receptive of a portion of said carrier wave, for

deriving from said carrier-.wave portion two constituent waves; a pair of non-linear impedances terminating the opposite ends of said wave-guide section, receptive of a modulation wave and said constituent waves, for deriving from the former two additional constituent waves, and combining the same, respectively, with said first-named constituent waves whereby. sideband Waves are produced; a second branch arm extending perpendicularly from said wave-guide section, perpendicularly to said first-named branch arm, re

cavity resonator." resonant to the frequency desired of said carrier-wave and receptivel of said y phase-shifted portion thereof, for altering the phase of said phase-shifted portion in response to any drift from said desired frequency; means,

receptive of said sideband waves and said phaseshifted carrier-'wave portion, for deriving from the former, constituent waves of opposite phase,

and `from the latter, constituent waves of similar phase; means, receptive of said oppositely and similarly phased constituent waves, fox` combining the same whereby, in the event no frequency drift has occurred, the resultant wave has the aforesaid selected amplitude characteristic, and in theevent a frequency drift has occurred,the

-resultant wave has a substantially different ampl'itude characteristic; means for deriving from said'last-named resultant wave a wave having an amplitude characteristic which is a function of the difference between the amplitude characteristic's of both said resultant waves; and means, receptive vof said di'erence-characteris'tics wave, for so tuning the source of said carrier wave as to compensate for said frequency drift.

12. Apparatus for stabilizing the frequency of a carrier wave comprising: a wave-guide section, having a perpendicularly extending branch arm receptive vof a portion of said carrier wave, for derivingfrom said carrier-wave portion two constituent waves; a pair of non-linear impedances terminating the opposite ends of said wave-guide section, receptive of a modulation wave and said constituent waves, for deriving from the former two additional constituent waves, and combining the same, respectively, with said first-named constituent waves whereby sideband Waves are produced; Aa second branch arm extending perpendicularly from said wave-guide section, perceptive of said sideband waves and portions of s said first-named constituentA waves reflected l from said non-linear impedances, for so combining the same as to suppress the carrier components thereof; means, receptive of another portion of said carrier wave, for shifting theA phase thereof through such an angle that, upon combination of said sideband Waves and said h phase-shifted carrier-wave portion, a wave havi .ing a selected amplitude characteristic results; a

ceptive of said sideband waves and portions of said first-named constituent waves reflected from said non-linear impedances, for so combining the same as to suppress the carrier components thereof; means, receptive of -another portion of said carrier wave, for shifting the phase thereof through such an angle that, upon combination of said sideband waves and said phase-shifted carrier-wave portion, -a Wave having a selected amplitude characteristic results; a cavity resonator,

resonant to the frequencydesired of said carrier wave and receptive of said phase-shifted portion thereof, for altering the phase of said phaseshifted portion in response to any drift from snaidv desired frequency; another wave-guide section, having a perpendicularly extending branch arm receptive of sideband waves, for deriving therefrom constituent waves of opposite phase; a

second branch arm ex'tending perpendicularly from'said last-named wave-guide section, perpendicularly to said first-named branch arm thereof, receptive of said phase-shifted carrierwave portion, for deriving therefrom constituent Waves of similar phase; l a pair of non-linear impedances terminating the' opposite ends of said last-named wave-guide section, receptive of said oppositely and similarly phased constituent waves, for combining. the same whereby, in the event no frequency drift has occurred, the resultant wave has the aforesaid selected ampli-i tude characteristic, and in the event a frequency drift has occurred, the resultantwave has a substantially different amplitude characteristic; means for deriving from said last-named resultant Wave a wavevhaving an amplitude characteristic which is a function of the difference between 13 the amplitude characteristics of both said resultant waves; and means, receptive of said difference-characteristics wave, for so tuning the source of said carrier wave as to compensate for said frequency drift.

13. Apparatus for stabilizing the frequency of a carrier wave comprising: a wave-guide system including two branches for dividing said carrier wave into two portions; said branches differing in electrical length by nA/4, where n is an odd integer and A is the wave-guide wavelength corresponding to the frequency desired of said carrier wave; means in one of said branches for deriving from the carrier-Wave portion traveling therethrough carrier-suppressed, sideband waves; means in the other of said branches for-shifting the phase of the carrier-wave portion traveling therethrough as a function of any drift in the frequency thereof; means for combining said sideband Waves and said phase-shifted carrier-wave portion whereby, in the event'no frequency drift has occurred, the resultant wave is of constant amplitude, and in the event a frequency drift has occurred, the resultant Wave is substantially amplitude modulated; means for deriving from said last-named resultant wave a wave whose sense and magnitude are functions, respectively, of the sense and magnitude of :any such frequency drift; and means, receptive of said last-named wave, for so tuning the source of said carrier wave as to compensate for any such frequency drift.

14. An apparatus for stabilizing the frequency of a carrier wave comprising: a wave-guide system including two branches for dividing said carrier wave into two portions; said branches differing in electrical length by nl/4, where n is an odd integer and A is the wave-guide wavelength corresponding to the frequency desired of said carrier wave; a balanced modulator in one of said branches for deriving from thev carrier-wave portion traveling therethrough carrier-suppressed, sideband wave; a cavity resonator, having a resonant frequency corresponding to the frequency desired of said carrier wave, in the other of said branches for shifting the phase of the carrier-wave portion traveling therethrough as a function of any drift in the frequency thereof; means for combining said sideband waves and said phase-shifted' carrier-wave portion whereby, in the event no frequency drift has occurred, the resultant wave is of constant amplitude, and in the event a frequency drift has occurred, the resultant wave is substantially amplitude modulated; means for deriving from said last-named resultant wave a wave whose sense and magnitude are functions, respectively, of the sense and magnitude of any such frequency drift; and means, receptive of said last-named wave, for so tuning the source of said carrier wave as to compensate for any such frequency drift.

GEORGE G. BRUCK. PAUL J. PONTECORVO.

REFERENCES CITED The following references are of record in the file of this patent;

UN'ITED STATES PATENTS Number Name Date 2,404,568 Don July 23, 1946 2,410,817 Ginzton Nov. 12, 1946 2,420,264 Rost et al May 6, 1947 

